Chemicals have been added to pools and other water supplies to disinfect and sanitize the water so that the quality of the water is useable for its intended purpose. There are a number of factors that affect water quality, including water chemistry parameters. The major chemistry parameters that are associated with maintaining water quality includes free available chlorine, total available chlorine, total hardness, total alkalinity, as well as pH. It is therefore important to monitor and control these chemistry parameters for water quality management, especially for water such as recreational and industrial water.
Chlorine disinfects or sanitizes water by destroying harmful microorganisms, such as bacteria, fungi, and viruses and also controls nuisance organisms, including algae that may be occur in recreational water, filtration device, and piping. Available chlorine is the major component of chlorine species, which is mainly composed of a class of chemicals that produce hypochlorous acid (HOCl), when is dissolved in water. When chlorine, either as gaseous chorine, sodium hypochlorite, or calcium hypochlorite dissolves in water it produces HOCl, and at the pH range of 5-6 chlorine exists as HOCl:Cl2+H2O=HOCl+H++Cl−NaOCl+H2O=HOCl+Na++OH−Ca(OCl)2+2H2O=Ca(OH)2+2HOClThe hypochlorous acid may then dissociate into hydrogen ions (H+) and hypochlorite ions (OCl−) and the hypochlorite ions (OCl−) become more predominant at higher pH of 7.2-7.5.HOCl=H++OCl−Chlorine in the forms of Cl2, HOCl, or OCl− is known as free available chlorine, and these three forms of chlorine may present in water and their relative amounts in water depends on pH and to a slight extent on temperature.
Combined available chlorine refers to any chlorine species associated with inorganic chloramines (NH2Cl and NHCl2) and organic chloramines (RNHCl, R=alkyl) in water. Total available chlorine is the sum of free available chlorine and combined available chlorine. The relative amount of combined available chlorine also depends on pH and temperature, and the concentration of inorganic or organic amines in water. However, the combined chlorine undergoes limited hydrolysis in water and has less oxidizing power than free available chlorine. It is therefore important to distinguish free available chlorine and combined available chlorine to measure the disinfection strength of residual chlorine.
Total hardness is the measure of water hardness. Calcium and Magnesium ions are the primary sources of water hardness. In general, calcium represents about 97% of the water hardness in pool water and the level of dissolved calcium is kept ideally between 200 to 500 ppm. Pool water requires the appropriate level of water hardness. High calcium hardness can result in cloudy water and scale formation due to the precipitation of calcium carbonate from the water, whereas low calcium can lead to corrosion.
Total alkalinity is the measure of the pool water's buffering capacity to resist pH change. The buffering capacity of alkalinity in water is due to carbonate, bicarbonate, hydroxide, and sometimes borates, silicates and phosphate, but is mainly measured by the amount of carbonate and bicarbonate in pool water. Further, at a desirable pH range of 7.2-7.6 in pool water most of the carbonate ions are in the bicarbonate ions from which buffering is provided. In general, total alkalinity is kept between 60-150 ppm depending on the sanitizing system being used and without a proper control of total alkalinity pH of the water rises or falls abruptly, causing the water to form scale and becomes cloudy or corrosive. The level of total alkalinity is tested and adjusted before adjusting pH.
There is a continuous interest in developing simple, rapid, and reliable methods for the determination of water chemistry parameters, including but not limited to free chlorine, combined chlorine, hardness, and total alkalinity. For example, because chlorine species in water are very reactive and may dissipate very quickly the reliable and accurate measurements of residual chlorine in water are difficult. There are a number of field test kits available for the determination of free and combined available chlorine in water, which is mostly based on the use of DPD (diethyl p-phenylenediamine). DPD test kits are manufactured with either liquid, powder or tablet reagents. Test kits that are currently available for the analysis of water hardness and total alkalinity are based on the use of specific dye reagents or acid-base indicators, followed by the spectrometric analysis or titration where changes in color in test solution are monitored. However, there are often interferences and human error in monitoring the color change for testing for hardness or alkalinity in water, leading to erroneous test results. At present, there are no simple, rapid, cost effective and reliable diagnostic test kits or devices to accurately and easily measure the contents of free chlorine, total chlorine, total hardness, and total alkalinity in recreational water. The present invention provides an answer to that need.